The present invention relates to improved piano plate mounting structure for an upright piano, and more particularly relates to an improved construction of a piano plate in relation to the associated action assemblies, side boards and keyboard assemblies on an upright piano.
In the construction of a conventional upright piano, its action bracket for action assemblies is coupled to a pin block on back posts and placed on a key bed. A keyboard assembly is also mounted to the key bed which is coupled to side boards by assistance of side arms. The side boards are supported by the back posts. Strings to be operated by the keyboard and action assemblies are all arranged on a metallic piano plate. In other words, among the three closely related members, the keyboard and action assemblies are placed under influence by behavior of back post and the strings are placed out of such an influence. Since back posts are usually made of woods, they are rather susceptible to changes in environmental factors such as temperature and humidity. Once any warp develops on the back posts due to such changes, it is liable to cause corresponding disorder in position of the keyboard and action assemblies relative to the strings on the piano plate which is usually made of metal and in general impervious to such emvironmental changes. This fact makes it very difficult to properly carry out dimensional setting and adjustment of these three closely related elements on the upright piano.
In addition, the piano plate is provided with a number of threaded holes for combination with related elements of the upright piano by assistance of set bolts. Since the piano plate is usually produced by casting, such threaded holes have to be formed by tapping or boring after casting. Hard texture in the surface region of such cast piano plate disenables easy and smooth formation of such threaded holes, thereby seriously lowering productivity of the piano plate and promoted fatique of cutters used for tapping and boring. Further, the heavy and unwieldy construction of the metallic piano plate requires hard work in its setting for these mechanical operations with use of lots of jigs.